science: chem

quarter 3

Atom

Smallest particle of an element that has the chemical properties of the element.

Nucleus

Found in the center of the atom.

Proton

Positively charged particle located in the nucleus.

Neutron

Uncharged particle located in the nucleus.

Electron

Negatively charged particle that moves outside the nucleus.

Democritus

Greek philosopher who proposed that matter could not be divided into smaller pieces forever.

Atomos

Small, hard particles that make up matter, as proposed by Democritus.

John Dalton's Atomic Theory (1803)

First atomic theory that states atoms are tiny, indivisible particles; atoms of the same element are identical; atoms of different elements are different; compounds form by combining atoms.

Isotopes

Atoms of the same element with different masses due to different numbers of neutrons.

JJ Thompson

Discovered electrons and proposed the Raisin Bun Model of the atom.

Raisin Bun Model

Model proposed by JJ Thompson, depicting atoms as having electrons embedded in a positively charged 'raisin bun'.

Ernest Rutherford

Discovered protons and the nucleus; conducted the gold foil experiment.

Gold Foil Experiment

Experiment demonstrating that most alpha particles passed through gold foil, indicating a dense center (nucleus) in atoms.

Neils Bohr

Improved Rutherford’s model; proposed that electrons move around the nucleus in specific layers or shells.

Quantum Theory

Theory proposed by Neils Bohr explaining the discrete energy levels of electrons around an atom’s nucleus.

Electron Cloud Model

Model proposed by Erwin Schrödinger, depicting electrons moving in a cloud around the nucleus without a defined path.

James Chadwick

Discovered the neutron, a particle with no charge located in the nucleus.

Atomic Number

Number of protons in the nucleus of an atom; in a neutral atom, it is equal to the number of electrons.

Atomic Mass Number

Sum of the numbers of protons and neutrons present in the nucleus of an atom.

Example: Chlorine (Cl)

Atomic mass number = 35, Atomic number = 17, Protons = 17, Electrons = 17, Neutrons = 18.